A solid oxide cell (SOFC) having a multilayer structure obtained by disposing an electrolyte layer (solid electrolyte layer) made of an ionically conductive solid oxide (oxide ion conductor) between a cathode (air electrode) and an anode (fuel electrode) is hopeful as a third-generation fuel cell. Cells of this type are being developed.
A solid oxide cell is a device in which a gas (fuel gas) containing a reducing agent, e.g., hydrogen (H2) or carbon monoxide (CO), and a hydrocarbon such as methane (CH4) is fed to the anode and a gas (e.g., air) containing an oxidizing agent such as, e.g., oxygen (O2) is fed to the cathode to thereby generate electricity (see, for example, the following patent document 1).
A solid oxide cell (SOFC) and a method of operating a solid oxide cell were proposed which each had a constitution capable of easily attaining a size reduction in power generation systems employing a solid oxide cell without fail (see patent document 2). This cell is a solid oxide cell in which an organic compound containing at least carbon and hydrogen as constituent elements is caused to undergo a pyrolysis reaction within the anode to obtain solid carbon and this solid carbon is utilized as a solid fuel (reducing agent) for power generation.
The solid carbon has the following features. Compared to liquid electrode active materials (reducing agents) or gaseous electrode active materials (reducing agents), the solid carbon has an exceedingly high energy density. It eliminates the necessity of a device constitution for feeding a liquid or gaseous electrode active material to the anode. The anode-side device constitution can hence be simplified.
However, the solid oxide cell described above has had drawbacks that the formation of solid carbon (hereinafter referred to as “activation”) necessitates much time, the amount of charge transfer obtained by one activation operation is small, and power generation after activation is low in output densitypower density and short in power generation time. In addition, introduction of a carrier gas for releasing outward a substance yielded on the fuel electrode during power generation has been necessary and this has been an obstacle to size reduction.
Patent Document 1: JP-A-9-129256
Patent Document 2: JP-A-2005-071717